TEMPERATURE RELATIONS OF AERIAL AND AQUATIC RESPIRATION IN SIX LITTORAL SNAILS IN RELATION TO THEIR VERTICAL ZONATION

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Abstract
Aerial and aquatic rates of O2 consumption were determined with polarographic O2 electrodes over 5.degree.-45.degree. C at 5.degree. C intervals for the marine sublittoral species, Acmaea testudinalis, Mitrella lunata and Lacuna vincta; and the intertidal species, Littorina obtusata, L littorea and L. saxatilis collected from Nobska and Manomet Points, Massachusetts, USA. A. testudinalis, L. vincta and M. lunata do not display metabolic adjustment to temperature. Aerial respiration in A. testudinalis is similar to, but averages only 36.4% of aquatic O2 uptake rates. L. obtusata, L. littorea and L. saxatilis have varying degrees of aerial and aquatic metabolic regulation with increasing temperature. L. obtusata, a low intertidal snail exposed to air for 15-45% of the tidal cycle, displays a respiratory pattern of passive endurance to high temperatures in air and water. L. littorea, the dominant snail of the midlittoral region, remains active when exposed to air (30-75% of the tidal cycle) and has a zone of metabolic regulation (Q10 .apprx. 1) between 20.degree.-30.degree. C. L. saxatilis from the upper littoral region is exposed to air for 70-95% of the tidal cycle and is characterized by a reversible torpor at > 25.degree. C up to its thermal maximum at 44.degree. C. For these 6 snail species, respiratory responses to increasing temperature are directly related to the pattern of vertical distribution in the intertidal environment. The temperature responses in respiration parallel the functional morphology of the pallial structures, and the physiological patterns of response to low O2 stress, as well as adaptive features of reproduction, larval development, water-control and nitrogenous excretion.